In order to build a defense, the GM cannot be a follow the ball one and his primary interest marketing and promoting the team. Every owner is focused on marketing and promoting his team, which is why they don't make good GM's.
This team's evaluation of FA D talent is not good and they're not much better in the draft.
The difference between Booger's philosophy of defense and that of Johnson's and Parcells is stark. Johnson used the 1st pick in the draft on a DT and Parcells made the best FA acquisition for a DT and I doubt if Booger would have done either.
Building a defense hasn't changed just because the offensive side has gone more to the air. It is still all about stopping the run first and that begins with the D Triangle, DT, MLB, DT. The Cowboys might, might, have one in Gallimore but they are missing the other two.
As evidenced by his "war daddy" remark, he sees defense as pass rush. He does not get taking the middle of the field away from the offenses.